A known problem in the field of telecommunications is that techniques useful in outdoor environments for determination the current position or location of a mobile telecommunications device, such as a mobile cellular telephone, are not effective for monitoring the position of the device in indoor environments.
For example, Global Positioning System device have been incorporated into mobile telephones to make use of GPS satellites to determine a phone's position. However, a relatively direct line of site to the satellites is required and the precision of the system is limited, thus making GPS generally unsuitable for positioning purposes in indoor environments.
It has been previously proposed to instead use dedicated systems employing different positioning solutions better suited for indoor environments, including systems where transmission and receipt of acoustic signals between the mobile device and a series of stationary satellites in the indoor environment is used to accurately determine the position of the device within that environment. Such prior art systems often use ultrasonic signals so as to be undetectable to the human ear, and include systems where the mobile device is the signal transmitter and the satellites are the signal receivers, and systems with the reverse configuration where the satellites emit the acoustic signals for detection thereof by the device.
As one example of the latter type, U.S. Patent Application No. 2009/0316529 assigned to Nokia Corporation, the entirety of which is incorporated herein by reference, discloses an acoustical positioning system in which a cellular telephone or other mobile device receives acoustic signals of ultrasonic frequency from a set of loudspeakers arranged to emit audio beacons in a predetermined sequence at predetermined intervals, and uses the time of arrival of the beacons to determine the device's position.
Applicant has developed their own unique system of this general type, in which sampled audio data collected by the microphone of the mobile phone is analyzed to identify sound level peaks in the ultrasonic range for use of those peaks as markers of the arrival of the ultrasonic signals at the phone. In such development, it has been found that inaccuracies in the position determination process can result due to misidentification of a located peak as the arrival time of a respective one of the ultrasonic signals from the transmitters, when in fact the peak in question is the result of a reflection of one of the signals.
Applicant has developed a unique signal processing method to address this complication by distinguishing the true arrival of the signal from such false positives in order to increase the accuracy and reliability of the positioning system.